Marine Le Pen is greeted with cheers before telling France she has no confidence in the country's leaders.
The far right candidate lost out to President Nicolas Sarkozy and Socialist Francois Hollande in the first round of presidential elections, but won a surprising 17.9 percent of the vote.
Ahead of run-offs on May 6, Sarkozy's camp has leaned right, trying to woo Le Pen's supporters.
But she withheld her coveted endorsement Tuesday, saying she'll cast a blank ballot.
(SOUNDBITE) (French) LEADER OF THE NATIONAL FRONT AND FORMER 2012 PRESIDENTIAL CANDIDATE MARINE LE PEN SAYING:
"So I have no confidence in, nor will I give a mandate to these two candidates, one of whom wants the right to win, the other the left to win; a united message which has meant that France has lost for thirty years. On Sunday, I'll cast a blank ballot, and in June I'll vote 'bleu-marine'."
Le Pen made the announcement at an annual celebration in honor of Joan of Arc that her party began in 1988.
Around half of Le Pen's supporters say they plan to vote for Sarkozy in the runoff, but the rest will either vote for Hollande or abstain.
Lindsey Parietti, Reuters